Objective: To explore the association between daytime outdoor physical activity (OPA) and oral health indicators among primary school students, aiming to provide evidence for developing oral health intervention strategies based on natural exposure. Methods: In October 2023, based on the "Tianchang Children s Light Exposure and Growth Development Cohort", 799 second and third grades children were recruited from two primary schools in Tianchang, Chuzhou City, Anhui Province. Physical activity intensity and light exposure were objectively monitored for 24 hours over 5 consecutive days using triaxial accelerometers synchronized with portable illuminance meters. Standardized oral examinations were performed to record dental caries, gingivitis, and malocclusion. Demographics, lifestyle variables, and household socioeconomic data were collected via questionnaires. Multiple linear regression (for the number of carious teeth) and Logistic regression (for gingivitis risk) were used to analyze the relationship between daytime outdoor moderate to vigorous physical activity (MVPA) and oral health outcomes. Results: The average daytime outdoor MVPA was (0.76±0.35)h, with (0.95±0.40)h on weekdays and (0.49±0.47)h on weekends. The detection rates for dental caries, gingivitis, and malocclusion were 31.0%, 4.6%, and 59.7%, respectively. Compared with children with good oral health, the duration of outdoor MVPA on school days was reduced in children with caries or gingivitis ( Z =-11.4, -5.01, both P <0.01). Multiple regression analysis showed that after adjusting for factors such as gender, age, body mass index, oral hygiene behaviors, an increase in daytime outdoor MVPA duration was associated with a decrease in the number of dental caries ( β=-0.64, 95%CI =-0.93 to -0.35) and a reduced risk of gingivitis ( OR= 0.58 , 95%CI =0.34-0.98) in primary school students (both P <0.05). The association was primarily observed on school days ( β=-0.72, 95%CI = -1.07 to -0.37; OR=0.42, 95%CI =0.21-0.85) (both P < 0.05). Conclusions Daytime outdoor MVPA on weekdays is significantly associated with a lower number of carious teeth and a reduced risk of gingivitis in primary school students. Increasing daytime outdoor activities on weekdays may serve as a promising and potential strategy for promoting children s oral health.